1. Field of the Invention
The present invention relates to optical components, and, in particular, to the manufacture of optical components used in laser-based optical communication systems.
2. Description of the Related Art
In a laser-based optical communication system, light is transmitted from a laser source (which converts electrical signals into optical signals) to an optical receiver (which converts the optical signals back into electrical signals) over optical fibers and through various types of optical components that modulate, filter, route, amplify, or otherwise process the optical signals. Two or more optical components may be aligned and mounted onto a substrate for an encapsulated laser package to be used in an optical communication system. One such component is an optical semi-isolator, which may be used in conjunction with an optical analyzer to form an optical isolator. Optical semi-isolators are described in more detail in U.S. Pat. No. 5,737,349.
FIG. 1 shows a cross-sectional view of a typical optical semi-isolator 100. Semi-isolator 100 is formed from two parts: a polarizer 102 and a rotator 104, each of which has an optical element mounted 20 within a frame. In particular, polarizer 102 comprises glass element 106 having an anti-reflection coating and mounted within frame 108, while rotator 104 comprises garnet element 110 having an anti-reflection coating and mounted within frame 112. Frames 108 and 112 are typically gold-coated metal structures. For example, in one implementation, frames 108 and 112 are iron-nickel (Fe--Ni) structures coated with nickel/gold (Ni/Au) plating 114.
Fabrication of semi-isolator 100 involves the following steps:
(1) Apply anti-reflection coatings to glass element 106 and garnet element 110; PA1 (2) Insert glass element 106 into frame 108 and insert garnet element 110 into frame 112; PA1 (3) Solder elements 106 and 110 within frames 108 and 112, respectively, using solder glass 116 at about 500.degree. C. in air to form polarizer 102 and rotator 104; and PA1 (4) Laser weld (118) frame 108 of polarizer 102 to frame 112 of rotator 104 to form semi-isolator 100.
Semi-isolator 100 may then be mounted onto a substrate to form one component of a laser package for use in an optical communication system. In particular, components like semi-isolator 100 are often auto-bonded to a ceramic substrate using a tin-lead (Sn-Pb) solder without using any flux. The ability to mount optical components like semi-isolators onto substrates without using any flux is important in applications where flux would adversely affect the operational characteristics of the optical elements (e.g., contaminate or otherwise interact with the surfaces of the optical elements).
Unfortunately, however, it has been found that optical components, such as semi-isolator 100 of FIG. 1, that are fabricated using a process similar to the one outlined above, cannot be mounted onto ceramic substrates with sufficient reliability using flux-less auto-bonding techniques. The strength of such bonding is often too low to withstand normal operational conditions (e.g., vibrations and temperature variations). As a result, an unacceptably high percentage of such optical components come loose from their substrates, thereby destroying the desired functionality of those laser packages.